Los Angeles battles 'largest wildfire in city history'

Hundreds evacuate as wildfire that has already burned more than 2,000 hectares threatens homes.

Local media said that at least three homes had been burned by Saturday evening [Kyle Grillot/Reuters]

The "largest [wildfire] in the history" of Los Angeles has forced hundreds to evacuate, the US city's mayor said.

Mayor Eric Garcetti told reporters on Saturday that the blaze, which broke out on Friday and lit up the hills surrounding the northern suburb of Burbank overnight, had already burned 5,000 acres (2,000 hectares).

More than 700 homes were evacuated in a north Los Angeles neighbourhood and nearby areas, officials said.

Officials warn the fire could make the air unhealthy to breathe [Kyle Grillot/Reuters]

The fire was only 10 percent contained with more than 500 firefighters battling it.

The blaze in thick brush that has not burned in decades was slowly creeping down a rugged hillside on Saturday towards houses, with temperatures in the area approaching 38 degrees Celsius, the Los Angeles Fire Department said in an alert.

The fire could make air unhealthy to breathe in parts of Los Angeles, the nation's second-largest city, and nearby suburbs, the South Coast Air Quality Management District said in an advisory.

Video posted online by local media showed the fire burning along a major highway as it broke out on Friday, with smoke hovering over the roadway as cars passed by flames a few dozen feet away. Officials quickly closed a stretch of the freeway.

California Governor Jerry Brown issued an emergency declaration on Friday to free up additional resources to battle the blaze.

Wildfires in the western US have burned more than 7.1 million acres (2.9 million hectares) since the beginning of the year, about 50 percent more than during the same time period in 2016, according to the National Interagency Fire Center.